1. Field of the Invention
This invention relates to a paper feeder for an image forming apparatus. More particularly, it relates to a paper feeder for an image forming apparatus such as an electrophotographic copying machine or a laser printer, especially to paper refeeder in an intermediate tray for an image forming apparatus capable of producing a composite image or images one each on the opposite sides of the copy paper.
2. Description of the Prior Art
In recent years, various image forming apparatuses have been developed, some of the type possessing a composite image function for producing different images in a composite pattern on one side of a copy paper and others of the type possessing a double-faced image function for producing images one each of the opposite sides of the copy paper. The effectuation of a function of this nature requires a copy paper having an image already formed thereon to be placed temporarily in an intermediate tray and then fed out again.
For examples, a copying machine disclosed in Japanese Patent Laid-Open SHO 62(1987)-6,269 will be described below with reference to FIG. 1. Paper storage cases 1 and paper feeding means 2 are disposed in the lower compartment and an intermediate tray unit 3 is disposed directly above the paper storage cases 1 mentioned above. An image forming part 5 centering around a photosensitive drum 4 is disposed in the middle compartment and an optical system 1 in the upper compartment. From the paper storage cases 1, copy papers are forwarded one by one to the image forming part 5 by the paper feeding means 2. A given image projected on the photosensitive drum 4 by the optical system 6 forms a reproduced image on one side of a copy paper. Then, the copy paper carrying the reproduced image is passed through a fixing part 7 and discharged as finished into a paper discharge tray 9 by switching means 8 or forwarded int the aforementioned intermediate tray unit 3.
The intermediate tray unit 3 is provided with an intermediate tray 10, switching means 11, a transfer passage 12 having two transferring rollers 120, and 121, a reverse passage 13, and paper refeeding means 14. It is so constructed that the copy paper brought in toward the intermediate tray unit 3 is transferred by the switching means 11 into the intermediate tray 10 either directly or via the transfer passage 12 and the reverse passage 13, and then fed out again by the paper refeeding means 14 to the image forming part 5. The paper refeeding means 14 is supported in a cantilever fashion, as illustrated in FIG. 2, by a roller shaft 17 projecting after the fashion of a cantilever and having a paper refeeding roller 15 rotatably supported on a holder 16. The holder 16 is supported on a rotary shaft 18 which is rotatably attached to the intermediate tray 10. This rotary shaft 18 is rotated in the direction of an arrow by driving means not shown in the diagram, with the rotation thereof transmitted to a paper refeeding roller 25 via pulleys 19, 20 and a timing belt 21. An operating lever 22 is relatively rotatably attached to one end of the rotary shaft 18 and is suitably stopped at a desired position by driving means 23. Thus, it allows the paper refeeding roller 15 to be positioned at any of the three, i.e. upper, middle, and lower, levels. In the construction described above, therefore, the paper refeeding roller 15 will be positioned on the upper level while the copy paper is being transferred through the reverse passage 13, on the middle level while the copy paper is being transferred directly from the switching means 21, and on the lower level while the copy paper is in the process of being refed.
During the course of the refeeding of the copy paper, regulating guide plates 24 regulate the opposite edge of copy papers P in the intermediate tray 10 as illustrated in FIG. 3 and the paper refeeding roller 15 sends the blank copy papers P out one by in the direction of nipping roller 25. When the copy paper P on the top is to be sent out by the paper refeeding roller 15, it tends to advance obliquely because it is susceptible of a few forms of resistance such as the frictional resistance produced between the lower side of the copy paper P in motion and the upper side of the next copy paper P, the adhesive resistance caused by static electricity, and the frictional resistance caused by the sliding contact of the paper P in motion with the guide members. Particularly when the copy papers are positioned by one side only, the paper P in motion is more liable to travel obliquely because the paper refeeding roller 15 cannot be disposed at the center of the stack of copy papers P. To prevent the paper P in motion from advancing obliquely, the regulating guide plates 24 are disposed in the manner described above.
The regulating guide plates 24 designed for the regulation under discussion, however, are incapable of precisely regulating the opposite edges of the copy papers P as illustrated in FIG. 4. When the paper P in motion has been heat curled owing to the travel thereof through the fixing part 7 (particularly so when the atmosphere is highly moist) or when the paper P in motion is thin and deficient in nurve. Thus, it is difficult to prevent the paper P in motion from advancing obliquely.
An object of this invention, therefore, is to provide a novel paper feeder for an image forming apparatus.
Another object of this invention is to provide a paper refeeder for an image forming apparatus, which by means of a simple mechanism enables a copy paper temporarily stored in an intermediate tray to be fed out without inducing any oblique advance, no matter whether the paper P is heat curled or lacks nurve.